I had the same problem a month ago and I was quite despaired . I did a lot of 'crawl around on your hands and knees ' , but when I was putting the sub at the supposed right place , it was still boomy and vibrating . The sub was always in a 90 degrees plan from the front wall or the side wall or even the back wall .
But, Saturday , a miracle happened !!!
I put it at 35 degrees on the side wall and approximatively 1' in front of the M60 . No more vibrations , very punchy and beautiful . So , depending of your room , the position is crucial . So , try it everywhere and in every angle .
Good luck ...
