Hi. I have an old Binatone uk fm cb that motorboats when i tx from channel 35 to 40 but not on the lower channels. It motorboats gradually worse as i go from 35 to 40, but doesn't do it when i turn the rf power down. In addition to this, it only motorboats for about 5 secs, the s meter fluctuates then it settles. Any ideas on what the fault could be please? Cheers.