Speaker problem

I do have a multimeter. I can test that. Wiring only the midrange and the Tweeter and then the bass. Do you want me to test the resistance while playing? 
No, it is not over the carpet. It is on the furniture. No, it does not make any sound before it goes down.

Today I am using a NAD m17 as preamp + classe sigma amp5 as amplifier and the speaker is a HTM2 from BW - 8ohms

Sorry, the speaker was disabling the amp channel no matter where. It did disabled the amp channel as front channel as center channel. It did disabled the amp channel at channel 1-2-3-4-5-6-7. The problem followed the speaker. Tried also changing cables from pre amp to amp and speaker cables

The problem is recent noted. I am not using the Yamaha anymore. When I upgraded with an amplifier that it first appeared. When it first appeared I was using the Yamaha 2030 as pre amp and the NAD M25 as an amplifier. At near -20 DB the speaker was showing the problem.  They told me by phone that it could be the Yamaha ( I don’t know how) and I replaced the Yamaha for a NAD M17 preamp. It kept happening of course. I thought it could be related with some issue with amp/speaker. I replaced the amplifier with a Classé AMP5. You might be asking: why you did not sent the speaker to repair? - I did. But the mother f... of the repair shop charged me for testing the speaker and told that it had nothing wrong. That is why