I get it to about 98% right by the workbench in Sanctuary Hills but can't find the source.

Anyone know where the devil the distress signal is coming from?

The signals can be above, below, or even inside buildings so don't forget to check any and all near by locations, as for this source. I'm not sure which one it is you're referring to, sorry.

Did you maybe by any chance put one of the picked up mission distress senders in your workbench?

Same issue here. I can get it to 99.64% and it has me standing in the road between my house and the workshop. There is nothing. I wrote it off as a glitch and turned off the radio.

Edit:

I've just loaded it up and I think I may have it cracked. I realised that the spot on the map is where I drop junk and scrap it (Local Leader Lv 1 doesn't seem to be working!).

I think there is a very good chance that I scrapped a Distress Beacon on that exact spot. Glitch?

Oh my - yes I kept a distress beacon and stored in the workbench DOH!!!!

Thanks Nunos - it was driving me crazy.

happy we could figure it out and you can walk your base in peace now

This is [censored].

I don't have a distress pulser in my workbench.

I was just passing through Taffington Boathouse and decided I'd turn off the radio beacon. I checked the workbench and there was a distress pulser in there but I did not have a distress signal on my radio channel. I took it out along with all the other junk for scrapping but kept the pulser in my inventory.

I returned to Sanctuary with the pulser. I am informed there is a distress signal on my radio. I check and it is the same one I can't find. I place the distress pulser on the floor and am informed there is a distress signal. I check my radio and there are now two signals, one for the one I can't find and one for the one I put down. I pick it up and the distress signal dissappears.

I drop it on the floor and scrap it. I now have two distress signals for distress pulsers that I have already completed and no longer exist in Sanctuary!

The distress pulser is only good for scrapping after you have found them and the only way you can scrap them is by putting them on the floor which activates the signal and leaves it activated after scrapping.

It isn't ruining my enjoyment of the game but it is a mistake on Bethesda's part that needs rectifying. An annoying niggle.

It took me a long time to find this post!

If there is a forum to report bugs I reckon you should post this in there, then it will be added to the fix list.