RELAY G55 losing signal power.

Recently I have found that my Relay G55 seems to be getting a weaker signal, so only putting out around 50%, compared to using a cable.

It's not down to any drop off, as it is still a constant signal, just weaker.

I have changed the cable going to my guitar, tried a new cable going out of my G55 to my Helix, and used non-rechargeable batteries, but it's made no difference. 

Has anyone else had this issue, and if so, how did you resolve it. 

Thanks in advance for any replies.

Vinny.