Lag stereobluetooth headset Motorola S9 HD on the street

Hi all. Just recently purchased a Bluetooth stereo headset (in the context of this post, headset) Motorola S9 HD. At the time of purchase, before you give the courier money, get them good and attester (connecter to an MP3 player iRiver SPINN and Google Nexus One). Everything was good :) Even ran the test on the range — put the player on the table and left for about 10 meters in the ears — the music played.
The fun started when I steer with new clothes to head home.

1) once out on the street — the music starts to stutter, slow down, etc listen to become not possible. The sound source is in the pocket of the jeans (the distance from ear to ear about a foot and a half turns)
2) Down in the subway — on the platform and the escalator lag
3) In the subway _not_ lag
4) get out of the subway to the street — again lag
5) Come home, the apartment is _not_ lag

It turns out such a pattern — in a closed room all is well (at work at the office, in the subway, in the apartment). As soon as I go out into the open — the sound starts to stutter and slow down.

What it can be? I would like to understand the physics of the process =)