Help: Crickets in the engine

[Storm59]

Has anyone run into this before?
I have a 2006 Chevy 2500 with an LBZ with Diablosport predator set at 85 and Allison. The engine or something in the engine comaprtment is making a noise like a few thousand crickets. the noise only happens at 1300 rpm. The noise disappears at 1250 and 1350. Usually running anywhere from 30 - 40 mph. I have had it into technicians and they replaced a cooler tube on the turbo and turned me loose. Only to have it reappear 3 blocks later. I have had this sound for about 8 months. I have not experienced any performance loss or malfunciton of engine or turbo. I have tried putting the tune back to stock but still no change. Noise only happens at this 1300 rpm under basically an idle load. it is quit noticable if you are drivin past a building with your window down. Quite annoying noise.
I see no oil leaks and cannot recreate the sound at neutral
I checked clamps on the intake (stock) as well as intercooler.
I am at a loss for ideas on what to look for.

 

[TheBac]

Check your belt tensioner and idler pulleys. Could have a bearing starting to go bad.

 

[paint94979]

it could very well be the "typewriter" sound... which is perfectly normal

 

[Storm59]

it could very well be the "typewriter" sound... which is perfectly normal

Actually that sound I like, this is like a hissing grinding noise but disappears except 1300 rpm under no real load. Asi isaid before i have not experienced and power loss or damage.
I am curious about the belt tensioner though.
Is there a way i can check that without the engine running or at an idle?

 

[TheBac]

Um, thats how you'd check them, engine off. You dont want your hands/fingers around that moving belt or pulleys, otherwise your wife just might be cutting your steaks for you from now on.
Once you loosen the belt, you just check the pulleys to make sure they still spin smoothly. If they are anything but butter-smooth, change them out. They have been found to be a wear item and really arent too expensive.

 

[Storm59]

So I have a question for you TheBAC. Why would the tensioner only make this noise at this rpm. Would this rpm cause a no load situation and take stress off the bearing causing it to make noise at only this rpm. Why wouldn't it make noise at other rpms? Whether under acceleration or under deceleration. My Curiousity his quite high.

 

[THEFERMANATOR]

I don't know about the LBZ, but I know the LB7's have the exhaust bracket over on the passenger side that atatches the downpipe to the engine and it is known to crack and make funny noises.

 

[TheBac]

So I have a question for you TheBAC. Why would the tensioner only make this noise at this rpm. Would this rpm cause a no load situation and take stress off the bearing causing it to make noise at only this rpm. Why wouldn't it make noise at other rpms? Whether under acceleration or under deceleration. My Curiousity his quite high.

They've been known to squeal only at startup, at low rpm, or whenever they feel like it. I just figure its a simple thing to check and eliminate as a problem. The way you describe the noise, and the age of your truck leads me to think that a bearing is starting to show signs. Sometimes its the simple things....

 

[Storm59]

They've been known to squeal only at startup, at low rpm, or whenever they feel like it. I just figure its a simple thing to check and eliminate as a problem. The way you describe the noise, and the age of your truck leads me to think that a bearing is starting to show signs. Sometimes its the simple things....

So I took of the belt and sure enough i think that both idlers as well as the tensioner pulley are going.
Do I have to buy the tensioner in order to get the pulley. it doesn't look like i would gave to but i'll ask anyway

 

[TheBac]

If you have the ability, you can replace the bearings themselves and save some money. RockAuto lists both tensioner and idler pulleys available, too....so your local parts place should be able to get them in.

Bearing info:

After 7.5 years and 105K miles, I figured it's time to replace bearings and belt before failure.
I set out to replace the bearings in my idler pullies and the tensioner pulley. All the grease in my pullies was gone, as I could spin pulley and it would freely rotate round and round and round, with a slight ringing sound, and slight play. A new pulley packed with grease will barely spin 1/4 to 1/2 turn.
As stated, the GM idler pulley, (GM #98072072), can be bought for $20 each. I went to 3 parts stores and none had the correct idler, and none had the tensioner pulley. I installed two new GM idlers, and replaced the bearings in the old, and now have two spare idlers.
Most people won't bother replacing these bearings, which cost about $8 each, but I did. Our idlers have a spacer shaft pressed in the bearing, which contains a pressed on dust shield. The spacer is bolted tight to engine, and the bearing allows the pulley to spin on it.
The original bearing was a NSK 6005OUL18A. The new bearing I bought was a Nachi Quest 6005-2NSE9. 47mm O.D. X 25 mm I.D. X 12 mm wide.

As for the tensioner pulley, if your tensioner is good, you can save money replacing this bearing, as the Dealer quoted $105ish for a GM tensioner. He stated the tensioner pulley alone was not available.
This bearing was very easy to replace, as it had no spacer or dust shield pressed in.
My old bearing was a NSK 6203DUL1BA. The new one I purchased was a RBI 6203-2RS/C3 for $5 each. 40mm O.D. X 17mm I.D. X 12mm wide.

As for the fan pulley bearings, they are dry also, as this one spins freely. I need to buy or fab a pulley holding tool to remove the fan, and then I will investagate and attempt replacing this bearing. This pulley appears to be pressed on, and may take some sort of puller to remove.
A new fan pully assembly for my LB7, (GM # 97226289), or the LLY, (GM# 97309640) cost $550, so just replacing the complete pulley would be expensive.

Also, some more bearing info:

Yesterday I bought 2 idlers for my Duramax at my local GMC/Buick/Pontiac dealership. They were $19.50 each plus tax. Both of mine were on the LB7 were tight and squeaky. One was nearly locked up.

I priced the bearing for the originals at the cost was $24.89 each. Then I have to spend the time to press them out, save the dust shield somehow, polish up the bushing and mic all those parts back in to get it like new.

Obviously its a money savings and time savings to just buy new ones. Even for a spare...its cheaper to buy a new one and keep it handy.

My tensioner pulley was still smooth but had some side play. The tensioner assy was still tight and and smooth in its swing arc. So I just polished off the dust and installed a new bearing into its pulley. I used a press to remove and a perfectly sized socket to install with a mallet. Using a press to install to bottom it out is risky to me. Could bend the pulley. It went together real easy. In this case the bearing was $8.46 and the new tensioner assy was $135. So here the savings is clear and the time was minimal. Good deal to do this one.

The bearings in both cases are NTN 6203LLC3EM for the tensioner pulley and NTN 6005LLC3EM for the idlers.

I also ordered a Gator Belt from Autozone. Know which amp alt you have (105 or 145) or duals, and if you have the EGR vacuum pump. There are four or more belt choices. I'll keep my old belt and the one idler that seemed still functional as an emergency backup. I'm going to soak the old idler in oil for a few days and try to force some oil onto the bearing just to see if it helps it.

 

[Storm59]

Any DIY tips for changing these tensioner and Idler pulleys?

 

[Storm59]

Well i am scratching my head again. I changed the tensionner- complete- as well as the idler pulleys and the soound is still there. At the same rpm 1300 and about 20 mph. Any Ideas on what to try next.

 

[JoshH]

Run it with the belt off and see if it makes the noise.

 

[Storm59]

Well i finally got a chance to run without the belt and the noise remains.

 

[ferramento]

My 07 LBZ work truck has this exact same problem. I have been fighting it for a few months as well. The truck has 128K and it has only gotten worse. But exactly like you say. Mine is 1400 rpm and light load like idleing through a parking lot or 25 mph down a road. I think it is coming from the exhaust clamp between the down pipe from the turbo to the exhaust or just around there. Must be a harmonics thing that has to do with the engine rpm and load.
But like you said I can't get it to do it parked. Even powerbraking it with someone under it won't show up. Has to be that perfect senario.
I'll let you know if I get to the bottom of it and if you find it please let me know.
I'm going to go look for that exhaust bracket that thefermanator suggested

 

[iwantone]

i know this was 2 years ago but anyone figure out the problem?

 

[LarryJewell]

exhaust leak at the gasket, either uppipes or manifold, look for evidence of soot