In call, Music on Hold plays in background

We had a client report a weird issue. They made an outbound call, with in 12 seconds of the call being answered their default music on hold music started to play in the background.

Client reported that they did not push any buttons durring the call. The only thing I see in the logs are the MoH start and the MoH stop.

Any suggestions on what caused this?

[2015-03-04 14:40:55] VERBOSE[6350][C-00001721] res_musiconhold.c: – Started music on hold, class ‘default’, on SIP/3705-000004bf
[2015-03-04 14:41:47] VERBOSE[6350][C-00001721] res_musiconhold.c: – Stopped music on hold on SIP/3705-000004bf