Three times now I have heard a short series of humming/harmonica sounds from that area. Sometimes it is accompanied by a sound like liquid boiling in a pan from that same location when the key is first turned on. It happened 3 days in a row during a spell of warm dry weather. My tech says he thinks the fuel accumulator may be developing a bad spring or diapraghm leak problem. It hasn't done it since the temperatures cooled down, so I haven't been able to chase it down any further.
2003 Firemist Red/grey leather SL 500
2015 Palladium Silver/black mbtex GLK 350
1987 Smoke Silver/burgundy mbtex 300E Sportline (SOLD)
Click to see 87 300E