Front end noise - 1997 E420

I'm looking for assistance diagnosing a front end noise on my 1997 E420 with 75k miles.

It's a muted, rumbling sound heard at low and medium speeds (up to about 50 mph) on most road surfaces. It's not constant, it comes and goes, it seems with minor changes in the road surface. There is no vibration or other unusual feeling in the steering wheel, and no adverse handling effects. So far, it's just a noise.

75k miles seems low for wear in suspension/steering parts. I did, however buy the car with 65k on it, and its likely that the prior owner didn't have all of the scheduled service done.

Are there servicable (greasable) steering or suspension parts on these cars, and might this help? And what might the dealer charge to fix this? Is it something that can be done at home in a well-equipped garage?

Thanks in advance!