Buzzing plenum

[RubbishFettler]

Good evening folks

I have got a noise coming from the plenum, which I can best describe as a low frequency buzz / vibration when revved above idle. Car is running fine, but I haven't heard it before. Has anybody else had this, or have any clue what it may be?

Cheers

Steve

[mrzigazaga]

Hi Steve...I get a hum type noise if i rev it and listen to it coming back to idle...However mine sounds more like its coming from the AFM which could be the flap spring groaning...Possibly..Maybe....

[SLB]

I had a light tapping noise a few years ago which was a loose trumpet. I put it back with some thread lock and I it has been fine ever since.

[Jack Valiant]

Classic symptom of a loose trumpet in the plenum had it on my old 400SE

[Number 7]

Easy enough to whip the plenum off to take a look (despite your username ). As said, could be a trumpet loose or fallen over.

[RubbishFettler]

Hi

Thanks for that, the thought had crossed my mind as there isn't much mechanical going on inside the plenum, and I had taken it off a few weeks ago to clean, so maybe I dislodged one. I'll take a look now that my thoughts have been confirmed by those in the know.

Steve

[adam quantrill]

Jack Valiant said:

Classic symptom of a loose trumpet in the plenum had it on my old 400SE

+1. Get some good trumpet glue.

[Wedg1e]

Outside chance it could be resonance caused by an air leak.

[ElvisWedgely]

How do you know the noise is coming from the plenum. The amount of noise my V8 makes when even idling, there's not much else I can hear under the bonnet let alone noise from the plenum. It could be one of many other things. Air leak, noisy alternator, power steering pump bearings,water pump or just simply something rattling. I would do a more thorough inspection before I go to the trouble of whipping the plenum off.

Tony. TCB.

[Wedg1e]

ElvisWedgely said:

How do you know the noise is coming from the plenum. The amount of noise my V8 makes when even idling, there's not much else I can hear under the bonnet let alone noise from the plenum. It could be one of many other things. Air leak, noisy alternator, power steering pump bearings,water pump or just simply something rattling. I would do a more thorough inspection before I go to the trouble of whipping the plenum off.

Tony. TCB.

My 390's so quiet I can hear the fuel injectors firing. And for the sake of six bolts and a big Jubilee clip it's hardly a lifetime's work to lift the plenum, surely? Quick smear of Hylomar on reassembly and your uncle Bob's your auntie's fanny

[RubbishFettler]

Hi Tony

I listened closely for the alternator, water pump etc. I put a screwdriver to the plenum and the handle against my ear. The noise was certainly from there. I will lift the plenum cover and check, as rightly pointed out, it isn't a big task