If I had an E34 M5 instead of my E34 525i, not only would I want to hear more noise, but I'd expect to hear more noise. I'm not sure about the size difference of your tires in regards to the width of the treads or the tread design itself, but your 525i probably had narrow tires. (my snow tires are on the factory rims, so I don't know the size off the top of my head because I just got the car and haven't looked at the snow tire sizes yet.) Here's what I know... I've got a fair bit of road noise because I have M5 *replica" rims that look like the ones on a E39, and they're much wider that stock, and they do make a lot of noise. I've got 235mm on the front, and 255mm on the rear, and they are loud, but the faster I go, the less noise I hear. If your engine is loud, I don't see the problem. You bought a sports car, and a damn fine one in my opinion, so it should sound like a sports car, right? I know these cars (5 series) are supposed to be quiet, so there may indeed be insulation missing off your firewall, but you should be able to tell just by jacking up the car and looking underneath and comparing the drivers side with the passenger side. One problem that may be festering is a worn wheel bearing humming away. Easy enough to detect differences in the two bearings with mechanics stethoscope. Anyways, congrats on your upgrade, it's cool to see you love the E34's so much even after 11 years! I'm working on 6 years of E30's and my first year of E34's.
