Yes, there is an oil trap. I just had mine begin to make a humming/howling kind of sound. I got the chance to be in contact with a certified Volvo mechanic and he told me of a simple check. Of course, your Check Engine Light is probably on and the sound is going to SEEM like its coming from the alternator.
The simple check: with the car running (and howling) pull the dip stick. If the sound stops, it is your oil trap. The part itself is not expensive. The mechanic told me that there is an oil trap extended warranty, which extends it to 10 years, 120,000 miles (whichever occurs first).Check with your dealer to see if you car qualifies.If you have/want to pay to get this done, you should probably prepare to bend over and take it a little. They have to disassemble the upper portion of the engine in order to get to the part.I am calling my dealer today to find out exactly what is covered under the warranty.One last thing, try not to let this go un-fixed for too long. You could blow some engine seals and cause oil to leak everywhere big time....left untouched or leaking long enough....you might get to buy a new engine!!