Grinding sound at Speed on 540 auto

Hey folks,

Got a mystery and looking for thoughts:

My '97 540 w/90K miles, automatic, w/recently replaced cats has a constant habit of rewarding me with a strange soft grinding sound (like water spraying at high pressure on plastic) when applying the gas above 40mph. Very intermittent, but much more audible at the lower 40mph-type speeds.

I swear the sound seems to be coming from the front passenger side, which makes me think wheel bearing, but the sound stops every time I let my foot off the gas, which makes me think transmission(?). It's almost guaranteed to happen more often going up a hill and while making a turn (right) - like on the on ramp to the highway. But it happens straight and level with my foot on the gas, too. And it's now happening almost all the time (60+% of the time)

Any insights or Wild-Ass-Guesses would be more than welcome and much appreciated.

Regards,
-M-

[billB]

Mark

For this kind of mileage it may be a good idea to replace the wheel bearings. If you experience a low rumbling sound, as if you have studded snow tires mounted, (how much of a difference this sounds from spraying water on plastic? to use your analogy) it is probably time to replace the bearings, unless, of course, you have studded snow tires installed! Germany stuff .Also, if you experience pad knock-back, it may be due to bad wheel bearings.

Testing: You can also test drive THE SOUND itself !! by turning slightly left/right while doing 50-60 MPH (no lane crossing please ) to increase the load on these bearing. The bad side will let you know. Now the sound may appear to you as comming from the front or the back (I learned NOT to trust my ears when it comes to bearings). A sound from a bad BMW bearing echoes in a 528i and a half direction so open the back seats pull it all the way down where you can see the trunk then drive it and do your famous 40-60 MPH. Doing so will pin point the source of the sound. Choices? either front or back bearings; in fact right or left REAR bearing ; you are open to the trunk????

Fixing: Front ones are hubs right/left the same part number. much easier than the back but watch out for the ABS sensors when pull down-make sure to disconnect 1st before pulling down (two hex screws). for the back ones you need a puller to get the new ones on the little shaft. and you may need it to pull the old ones out. the outer ring gets separated from the bearing assembly when you try to pull it out.
goodluck

p.s. do you need detialed instructions on how to do it? let us know
BILL