undesired Oscillation problem

Hi guys
I had a problem, when I tested my FM receiver chips, there is an undesired signal around 250KHZ at 20 mV, I did not know where it comes from. One of suspection is from amplifer which might oscillator. I attached my anplifier design, can anyone give me some idea how to test in software if this part is easy to oscillator.
Also what will be a possible noise origan in RF chips? I have mixer and oscillator(current starving inverter oscillator) too. Please add as much comments as you can. How to find if the attached file is easy to oscillate or not in software?
Thanks a lot

Is "Vbias" supplied by an external voltage source ?
Or as I saw, three gates are connected between them ?

yes,Vbias is supplies by an external voltage source. Also, the oscillation signal is at (Vdc Vac 15mv) in the graph and it can be amplified by amplifier. I am not sure where the oscillation come from yet, but it is likely come from this amplifier, Any suggestions?
Thanks