Noise on releasing gas pedal after changing alternator

[forderit]

I recently changed alternator, alternator belt and AC belt, now the engine makes an unusual noise upon releasing the gas pedal while driving. I filmed this video with one foot on pedal and another on gas to demonstrate the noise, I can’t wait yo know what is wrong: Watch video on youtube
Update: Took the car back to same garage, they assumed one of the interlocutor pipes may be faulty, so they changed it, the noise persists and can be heard on releasing the gas pedal and sometimes noise when going on a bump, it sounds like a screw that was left loose or friction. Any ideas appreciated.

[huron]

Just looking at the video your top engine mount is gone. It shouldn't move around like that.

[37 RUBY]

Diagnosis from a distance always fraught with danger....but to me that sounds like the alternator pulley clutch.

Did the new alternator come with new pulley or was your old one transferred?

Why did you change the alternator?

[abdiel]

Originally Posted by huron

Just looking at the video your top engine mount is gone. It shouldn't move around like that.

Yep, as Huron says your top engine mount is totally U/S. Get it replaced ASAP.

[scbamber]

You need to change your garage too! Fancy missing that top mount

[Laird Scooby]

First suggestion i'd make is remew that top mount, it sounds as if the exhaust has a minor split in the flexi that may or may not be leaking gas but because the engine is moving around like a frog on a hot plate, it's likely to get worse.
Change the mout and see what happens, also investigate your downpipe/flexi section of exhaust.

[37 RUBY]

I respectfully disagree with the train of thought that the engine mount is causing a pipe to expand/stretch then leak.

I have listened back to the video. It really does sound like a dry bearing. If the aux belt tensioner pulley or alternator pulley is seizing I would expect to see marks on the belt face and grooved side as the belt is forced to skid round.
If so it needs attending to asap. You don't want a pulley seizing up then destroying the new belt, bits of which could get under the cam belt and destroy the engine.

I know you've had new belts but what about the tensioner pulley and alternator pulley?

Alternatively, is that worn engine mount causing a pulley to catch on something. If so there should be witness marks on one of the pulleys.

...and yes get that mount sorted so you can rule it out. You could always cut some wood to place as temporary stops into the mount to limit its movement then perform the same test.

Let us know how you get on.

[Laird Scooby]

That's fine, i have however seen an exhaust break slightly due to a worn/broekn engine mount such as that and create similar noise. Let's face it, as someone else pointed out further up, remtoote diagnosis is more or less a guessing game.

Just putting my idea forward as it sounds very much like what i heard before (except that was a 90 deg V6 with a similar "dog-bone" engine mount, more of a movement damper really, gone) and had broken the flexi on one side (the bottom of it) so it was opening up when the engine revved or was under load and rejoining when idle/cruising.

I can see why you say it sounds like a dry bearing or unintentional pulley contact due to rocking, similar thoughts crossed my mind but i went for what i thought was the most likely scenario.

Bear in mind, the OP may not have been quite so "rigorous" with his testing as the garage was and the garage possibly finished the crack in the exhaust with their testing of the alternator, especially as the noise seems to have appeared since they worked on it.

Who knows, we might both be right and we could both be wrong!

[37 RUBY]

Originally Posted by Laird Scooby

Let's face it, as someone else pointed out further up, remtoote diagnosis is more or less a guessing game.

Yeah that was me

Originally Posted by Laird Scooby

Who knows, we might both be right and we could both be wrong!

We need to work on our worldwide beer token stash...the last ones you and me earned were in Norway. This time we might earn some Adnams of Suffolk beer
tokens.

[Laird Scooby]

Originally Posted by 37 RUBY

Yeah that was me



We need to work on our worldwide beer token stash...the last ones you and me earned were in Norway. This time we might earn some Adnams of Suffolk beer
tokens.

More like Fullers London Pride looking at the OPs location!
Long time since i had a few pints of Abbott, lovely drop of stuff!