You cannot detect silence directly, but you can detect short call duration, while amount of call drops and amount of outgoing HO are small.
In other words : calls are released shortly after they are established.
1/ Check average TCH duration in the cell (or per TRX)
2/ Check average A-interface timeslot usage.
The 1st method works if the problem lies in the cell or in the BSC
The 2nd method works if the problem of silence comes from a problem of A interface timeslot configuration.
It is probably the 2nd method that will show the best results, because it is highly probable the problem occurs only on few A-intf TS.
If working with alcatel equipements, check out the method here :