This report could be classed with 'Transmitters', 'Antennas', or 'Receivers', so we'll put it here with 'General Radio Discussion'.
Multipath is a complex interference event when main signal reception is interfered with by reflected signal causing signal loss or distortion.
Here at my desk is a Sangean ATS 505 used to monitor our daily program schedule from KDX-FM, broadcast from an indoor bamboo tower in the next room. It worked well until a few days ago when I moved some boxes and an out-of-service computer tower to a location at the foot of the tower. Since then, whenever I placed my hands over the keyboard on my desk the multipath interference got so bad it sounded like a wood shredder.
The fix turned out to be easy. I moved the out-of-service computer tower 1-foot and turned it at a different angle. Result: no multipath whatsoever.