Sennheiser XSW 1-835 Dual A-Band Vocal

We have used Sennheiser in our band for many years, Since we needed a couple more mics for rehearsals (small gigs) we thought this would be a great choice. The units are super light and they feel a bit "cheap" but the worst part is the performance, in many cases, there is a "blast" which seems to be interference with other signals. (Never had that issue before) Even when scanning 3 or 4 times the signal keeps being shockingly interfered with a super loud blast. I am very unhappy with the product, our engineers tried everything, but nothing has helped.