Have you decoupled the psu rails close to the device with caps and rf chokes ?. The rf must be getting into the op amp somewhere, so keeping the layout as compact as possible, with short decoupling paths from device to ground plane may help. It doesn't take much lead length to resonate at 144Mhz. The other question is what power level is the tx running at and how close is the op amp to the op stage ?. If you are running at anything more than a few 10's of milliwatts, you will need screening around any adjacent low level stuff, especially at vhf.
I built some hf linear amps in the 100 watt region some years ago and the rf just gets everywhere if you don't pay attention to decoupling and screening...
Regards,
Chris