Buzzing Noise From Engine Compartment

[glc24]

Usually I find answers to my questions just by searching the forums.But I can't seem to find an answer to this one.I have a '98 K1500 5.7 Vortec going on 149,000.The only failure I've had so far (knock wood) is a fuel pump. A couple of weeks ago,I noticed ( for lack of a better description) a type of "buzzing" noise coming from somewhere on the top end of the engine. I can't
seem to pinpoint it. I've only noticed it at idle and I've never heard it on a cold engine. It doesn't do it all the time either. The truck runs fine and I've never had a check engine light.All sensors and components are still original.
I can't think of anything else that might be helpful info. If someone has had
the same problem or if someone knows from experience what it might be,I would appreciate a response.

Thanks
Greg

[derekbitt]

I have basically the same truck, i dont have this problem, but try to eliminate the pvc valve possiblity and then at the top of the engine is the fuel injector system. i can imagine both of these may make buzzing. you could get an engine stethescope or a piece of rubber hose to listen to a specific part of the engine to narrow the search. could it be a fast mechanical sound or is it more of an electrical buzzing?

[glc24]

Thanks for the reply derekbitt. I did replace the pcv.
I really can't say what it exactly sounds like,it could be both of what you suggested.The more I hear it,the sound is like taking a electric motor with a bad bearing (the squeal),lining a box with insulation and putting the motor in it and closing it up.It has that type of muffled sound. I checked all the rotating parts on the engine and they seem fine. I think I will try your rubber hose listening device.

Thanks
Greg

[jj76ta]

I'm not positive but check the egr valve. These are elecric and operate when the engine has warmed up. Just a suggestion. I would do the stethiscope test to find the area the noise is coming from.Good luck.

[horse482]

Have you checked the cap and rotor, if the distributor bushings get loose, then it lets the rotor touch the contacts in the cap creating a buzzing noise.

[glc24]

Originally Posted by horse482

Have you checked the cap and rotor, if the distributor bushings get loose, then it lets the rotor touch the contacts in the cap creating a buzzing noise.

I may be wrong,but wouldn't the engine run very rough or sputter once in awhile or worse. I just tuned it in the early spring,and didn't notice any play.
I will check just to be sure.

Thanks
Greg