Uniden GMR1635-2

Hello

I have a pair of the Uniden GMR1635-2 two-way radios. They are fairly old but havn’t used them ever. Just opened the original packing.

One of the walkie talkies is emitting a static sound around every 5 seconds which lasts for one half a second.
Once around 5 seconds has passed it emits it again for half a second and it keeps happening.

I notice sometimes it does not happen after using it for a long amount time.

It sounds like TV static. Sometimes it can be faint or sometimes it can be quite loud.

The problem is only in ONE of the two radios. I have tried changing batteries also but the same problem persists.
Any suggestions?

Thanks.