I have posted this in another forum, but wanted to post in this one to see if I could get some more help. I have a 99 clk430 that started whining when you rev the motor. You can be sitting still and rev the motor and it whines. I have had the waterpump and power steering pump check, both were showing signs that they had leaked, so I replaced them. In doing so, we noticed that there was quite a bit of play in the tensioner pulley. so, we went ahead and replace it as well. But, I still have a whine. Sometimes it will be better and other times worse. I thought for sure that one of the two pumps that we relaced, since they were leaking, would be culprit. I had the suggestion from the other forum to check the reservoir and see if the fluid swirled while running. It does not. I am at a loss as to what it could be, but it is annoying as heck to listen to. Has anyone ever had this problem and if so, what could it be? Could it be the idler pulley? It does not appear to be the tranny because I had the tranny checked a few months ago and was told by the mechanic that the tranny looked almost like new on the inside. The noise to me appears to be external to the main motor. Thanks for all the help I have gotten from the other forum and to anyone here that can help me figure this out.