Noise is RF AGC try it.
Also try turning down the modulator if you can. If not unhook it & put
4' of wire on it & go OTA with it. . It will probably clear up.
OR hook a VCR to it.
If its not an external problem odds are its the IC.
Pins 3 & 4 are used. Pin 4 shows 2 voltages. One is for zero signal
the other is strong signal. It should change when mod is switched on
& off.
Also run the set & see if the IC is getting hot. Should be just warm.
You should also check the resistors off pins 3 & 4 before changing the IC.
Thats about all I can do long distance, maybe others have ideas.
Good luck & let us know how you do.
73 Zeno
LFOD !