[TowerTalk] Receive level issue-could it be in the antenna system?

[John G.]

I have an Icom 706 original which I have owned for the past 2 years and really like (other than the NB not being that good on consumer electrical noise).  I have noticed for the past few months that the receive seems to drop at times on certain bands-it started on 12m and now occurs on 15m as well, and has started to show up on other bands, like 17m and 30m for the first time last night. If  you click the key or mic to quickly put it into transmit the receive comes back.   To me this sounds like a dirty relay or one that is going bad.  

Someone did suggest to me that it could be a problem in the antenna system as well. I did some checking this morning, and have determined that it isn't in the low pass filter, the MFJ tuner, or any jumper coaxes in the shack.  It would have to be in the feedline going to the G5RV, or the balun there.  I haven't had time to change out the coax run yet.  Would an antenna problem affect some bands more than others?  I use the same antenna and feedline for all HF bands.

I have also noticed that on 12m and 15m the receive will come back up by itself at times.  Sometimes it is a quick drop down and come back several times in succession.  Would a relay problem do this?

So, with this latest information, what is the better guess as to the problem-in the rig or the antenna system?

73 John AF5CC