General: Odd noise, aux belt area

[zodski]

I've looked through a lot of the posts here, and cannot find one that matches my symptoms. So here I go.

I've had my V70, '03 reg for 8 months. Its reached 94.000 miles, and the dealer that I bought it off tells me it has a proper service history, with one (confirmed) previous owner. Recently (within the last two weeks), a serious noise has started to make itself apparent. Imagine someone running along a metal railing with a stick - you get a 'tat-tat-tat' sound. The frequency is quite fast, and gets faster as the engine accelerates. It starts immediately with engine start, and doesn't get any better during a trip. Its loud enough to turn the occasional head as I drive through town. When I take my foot off the accelerator whilst in motion, it almost disappears, but reappears as soon as I put my foot back on the accelerator. At higher speeds it is quieter. At idle, its very noisy.

So I lifted the hood, and worked out that the noise came from the aux. belt area of the engine. Touching the pumps/alternator didn't help identify the source, as the noise appears to be transmitted through the block. Triangulating, I THINK the alternator is to blame, but cannot be certain. Even listening with a metal bar to all the rotating components doesn't narrow down the source. Incidentally, the belt wasn't vibrating noticeably at idle - it looked smooth at all times.

So I took the aux. belt off, and removed the alternator (3 hours trying to get it out!). I checked the pulley, and it rotated freely both ways, and engaged the armature when given the 'flick' test (cannot remember which way worked, but I know one way caught the armature,the other left it alone). I also checked the bushes, on the grounds that if one is too short it might load/unload the alternator as it spins, causing this noise (is this likely?). One bush is AT minimum (5mm) and the other is about 9mm. I've put everything back, and the noise hasn't gone.

I cannot find anything on the forum that describes these symptoms, and I cannot afford to splash out on random parts. My experience of my local dealers, in the main, is that they have a stab, then move onto something else as a cause. I find the expertise on the forum much more reliable, with great suggestions, so I have come here for advice rather than the dealer. Does anyone have any suggestions, or advice to give, on what the cause might be? Thanks in advance.

[Nick44]

Did you try running the engine with the aux belt off?
Thos would prove out all aux components, alternator, PAS and Aircon, as well as the aux belt tensioner itself.

[chiptivo]

Dual mass fly wheel? They apparently sound like a bag of spanners when they start to go. ?

[zodski]

Originally Posted by Nick44

Did you try running the engine with the aux belt off?
Thos would prove out all aux components, alternator, PAS and Aircon, as well as the aux belt tensioner itself.

Thanks for the suggestion - I thought of this, but wasn't sure if this was safe to do. I'll try this tomorrow.

[zodski]

Originally Posted by chiptivo

Dual mass fly wheel? They apparently sound like a bag of scanners when they start to go. ?

Never heard of these - can you tell me what the implications might be? Thanks.

[Nick44]

Chiptivo has a good point.
Your noise could be being transmitted through the crankshaft.

My test with the aux belt off will prove, nothing to harm if you do this, but DON'T try and drive it with the belt off, and don't run the engine for too long.

DMF stands for Dual Mass Flywheel.
Is yours auto or manual?
If auto forget the DMF, auto's don't have them.

If manual, the DMF is does the traditional thing a flywheel does, i.e has weight to carry the engine through the suck-squeeze-bang-blow and iron out inherent lumpiness.
DMF's have a dynamic weight that can move during the cycle so still smoothing the engine but for less mass, so more efficient, but no longer a simple weight so there is stuff to break/wear - also like everything else modern, more money when it breaks.

[grass hopper]

just a thought,dos it sound like this ?

http://www.volvoforums.org.uk/showthread.php?t=102413

[zodski]

Originally Posted by Nick44

Chiptivo has a good point.
Your noise could be being transmitted through the crankshaft.

My test with the aux belt off will prove, nothing to harm if you do this, but DON'T try and drive it with the belt off, and don't run the engine for too long.

DMF stands for Dual Mass Flywheel.
Is yours auto or manual?
If auto forget the DMF, auto's don't have them.

If manual, the DMF is does the traditional thing a flywheel does, i.e has weight to carry the engine through the suck-squeeze-bang-blow and iron out inherent lumpiness.
DMF's have a dynamic weight that can move during the cycle so still smoothing the engine but for less mass, so more efficient, but no longer a simple weight so there is stuff to break/wear - also like everything else modern, more money when it breaks.

Thanks for the quick reply. My car is an automatic, so assume there is no DMF to worry about?

[zodski]

Originally Posted by grass hopper

just a thought,dos it sound like this ?

http://www.volvoforums.org.uk/showthread.php?t=102413

Thanks for the link. My car has a much faster sound, nothing like that.

Should have thought of posting a sample like this...I'll do it tomorrow.

[Nick44]

Automatic = No DMF.
That's worth a