Noisy Engine
 

Recently bought an '04 TL with about 76,000 miles on it. I've noticed that, especially when cold, the engine seems to rattle.

I've heard that this might happen when using low octane gas but I've always used premium. Link below is to a recording of what it sounds like. I figured I'd see what recommendations I could get here before taking it in to be looked at.

Everything seems to be working fine, I'm just concerned that this noise might mean something bad.

http://www.jasonskidmore.com/acura/car-sound.mp3

Forgot to add. This was recorded when the engine was at idle. I don't usually notice it much, if at all, at highway speeds.

Did you have a mechanic check the car out before you bought it?
Sounds to me like someone may need a valve adjustment.

Have you checked the oil? Too low on oil could mean trouble as well.

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It could be anything from a hurt piston to a cracked flexplate or loose torque convertor bolts to a bad serpentine/timing belt tensioner.

To eliminate or confirm a piston, pull one coil wire at a time. Piston noise will usually go away or get much quieter when you find the cylinder that was making the noise. If the noise does not change after pulling each coil wire one at a time I would start looking in the belt area first and then the transmission/flywheel area.

Sorry I posted this right when I woke up. You might try removing the serpentine belt and starting it to see if the noise goes away before pulling each coil. Both are very easy to do but the belt probably has a better chance of solving the problem.

Can you tell where the noise is coming from?

Thanks for the replies. I'm not very mechanically-inclined. I went by a smaller shop where I've had my other car worked on and the mechanic seemed to think it was the oil pump. I got a second opinion from a mechanic at an acura dealership who thinks that it's the tensioner on the timing belt because of the way it sounds when revving up/down.

I'm only at 81k miles but if there's a chance it's a timing belt issue I'm probably just going to bite the bullet and get the timing belt/water pump changed.

It could be, but I doubt it. It's more likely the auto-tensioner for the drive belt (serpentine belt). Have you mechanic remove the drive belt and then start the engine. If the sound is gone, it's either the AT, a pulley/s on the AT, or the belt.

Remove the drive belt first. It takes 10 seconds to do. Fire it up, see if the sound is gone.

Solved: Bad timing belt tensioner
 

Thanks, everyone, for your responses. The mystery is solved!

I ended up taking the TL by a repair shop I've used before. They looked at it for 2-3 minutes and concluded that it was the oil pump. I knew better.

Took it by an Acura dealership and their techs thought it sounded like slack in the timing belt. Instead of paying $1100 + tax at the dealership I took it to a local shop and here's what they found/did:

The timing belt tensioner had rusted and wasn't keeping tension on the belt. Pieces of the belt had fallen off and it was probably very close to breaking. They replaced the belt, tensioner, water pump, I think an idler pulley that were all in the same area. I also had a bad engine mount that they replaced since they already were in that area.

Total bill: $1100 after $20 disposal fee & $90 tax
About $500-ish in parts & $400-ish in labor

Noticed a HUGE difference when I started it. It sounds brand new. Looks like I'm getting slightly better gas mileage now, not sure if that's related.