UHF problems

Is it possible your antenna has a break internally?...
Or a bad connection on the base?...

I have checked the connections and they seem OK , the antenna is one of those two piece ss wire ones and appears to be OK.
Could it just be time for a new unit ? I'd hate to replace the thing every two years though ............

Thanks for the tip ! Will try that .....

As already said - check your wireing to the aerial. The earth connection often corodes and does not make a good connection.

It's possible your radio is suffering from something called microphonics.
This is where vibration from the vehicle eg. road, transmission, engine is transfered to the radio via it's bracket and makes components in the radio vibrate. This can then affect the transmitted audio. A quick check is to remove the radio from the bracket and support it without direct physical connection eg with a cushion or towel. You might need to get some help from someone for this test. You can even tap the radio while transmitting and see if the people on the other end can "hear" the tapping.
If the interference goes away during this test then it's a trip to the service shop to fix the problem.
How is the UHF mounted? Does it get hot? Some Uniden radios have a small wax filled metal box which contains vibration sensitive components. If the radio gets hot, this wax can melt and move away from where it should be. Radios mounted in dash pods suffer badly from heat related faults.

Have simular problem some times with the same unit

The problem i find is that the mic lead has come loose & needs a clean & tighten
& works well for mounths again

Many thanks to you guys that took the time to respond ! Looks like a little Saturday morning mission will be coming up this week.