Just the other day I noticed a knuckle cracking sound coming from the front end of my 1992 W124 300TE 4Matic wagon. I can't tell if it's coming from the wheels or under the engine, but it is definitely connected to the turning of the wheels. I only seem to hear it at low speeds, it happens in both forward and reverse, but not all the time - it seems to come and go. Often, the wheel needs to make a full revolution from a full stop before the noise arises, but not always. This evening I didn't hear it at all on the drive home until I pulled into the garage. The wagon has almost 140,000 miles on it. Around 105,000, the left & right front axle and inner CV joint boots were replaced, but as long as I've owned the car, (approx. since 95,000), I have never replaced the front wheel bearings or tie rod bushing. I did a search here and found nothing, other than it doesn't sound like the noise of a bad bearing. Any thoughts? I'm stumped.

1962 MB 220SEb "Fintail" Sedan
1992 MB 300TE 4Matic Wagon
1995 Subaru Wagon AWD