S60 2.5T AWD

SO as you may have seen on the news recently... Denver had a few days of extreme cold temperatures down in the -* in the morning. Well, during these temperatures when the car was frozen solid it had no issues starting up. I would let it warm up a notch, rev it to between 2 and 3k. No issues at all. When the temp gauge started to move I would head off to work. This is where the problems started.

So,

1) When I'm at a stop I can rev the engine with no knocking sound.
2) When I'm in drive and moving the sound progressively would get louder between 1500 and 3000 (didn't go any higher) depending on how cold the car still was.
3) Once the car was warmed up about 3/4 of the way to normal operating temps and after a mile of driving through the neighborhood the clanking would be gone all together.

So after I found this out, in the mornings I would sit in the driveway with a steady rev at 2k rpms until the car was warmed up about 3/4 of the way again. When I put it in drive and took off sometimes the clank would happen during the same conditions, but at normal operating temps and after a mile of driving I wouldn't hear it again.

Does anyone have any ideas as to what could be going on?

I'm not a mechanic or anything but I've kind of come to these conclusions/observations so far...
1) The knocking sounded like an abused engine that needed oil and would increase/decrease with the drive power. However, I don't think it's an engine issue because I can rev it just fine while in park with no knocking sounds.
2) I think it may be something to do with the drivetrain somewhere but have no idea...
3) I would also say that at about 20* and above I don't experience any of these issues from a cold start and drive with no warm-up period.

 

This sounds similar to the problem I am having (2002 S40). Did you ever find the solution. I am guessing altenator bearings, or idler/tensioner pulleys.

 

Does yours make a sound while sitting in park and revving?

Long story short... I haven't figure it out yet. At one point this January I had that sound and a seizing sound that occurred while parked (which turned out to be my alternator going bad.) I also had them look into the knocking sound and they thought it could have been an exhaust leak (loose bolts.) So, I had them look into it and sure enough, some bolts were lose. They tightened it up and I thought all was good until a few weeks later when it got cold enough and I heard the noise again. I have no idea what the issue is. They even took a look at my drivetrain and they said it all looks fine. If you find anything out please let me know. I don't think it could be an idler/tensioner pulley because the noise doesn't occur unless I'm accelerating down the road in drive. I can sit in the driveway and rev as much as I want and it doesn't make a peep until I put it in drive and go down the road.

 

The sound doesnt increase upon acceleration. At idle its loudest (800 rpm) - however, if if I apply a little gas (1500 rpm) the sound does go away. After 5 minutes, when the car is warmer, it goes away. I have to assume its some sort of hydraulic fluid warming up. I'll let you know if I found out.