My 95 C280 makes 2 noises or warning sounds.
The first being the buzzer. Lights are on (or key in position 1) and door is open, and the seatbelt reminder.
The second being a beeping sound (same warning tone on all newer Mercedes in lieu of buzzer too). Meaning parking brake is applied and the car is going more than 3 mph.
Maybe it thought the parking brake was on if it was that beeping? But I would think that the Brake Light (dash reminder) would have also been on. But I'm also not sure if a 92 E had that same tone or parking brake reminder, or if that's the same tone you heard.
2006 E350 w/ 155k miles (Daily Driver)
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)