1992 500SL
All break lights functioning well except for the middle trunk light which has never worked in the last 5-10 years
I removed the passenger airbag thinking the chime was behind that -- nothing behind there -
I opened up the center panel at the top of the dashboard where the security system is and the chime seems to be coming from in or behind that panel --
when the car is in gear and rolling in reverse or forward the chime starts pinging and wont stop --
also, in reverse the little yellow wheel lgiht by the speedo flickers that that monitors the wheels not rolling in sync -- that never used to come on either
-- the car never did any of this before putting it into storage -- a year ago
and the SRS light is on all the time now too, I'm wondering if the two are inter-related..

The chime is located on the rear of the instrument cluster.

I don't know the early instrument clusters very well however I seem to remember they have issues like you describe. ( capacitor issues / ground / internal voltage regulator ? )