amplifier - Where might the noise be coming from in this speaker driver circuit?

Well, it will be a broad schematic. To summarize, there my approach is:

1. Yellow part is for oscilations at three different freqs(around 0.8 - 2 kHz, different for each of the three signals), sinusoidal, I can get nice 6 Vpeak sine waves, observed with oscilloscope, no noise, smooth.


2. In the orange part, I use classical potentiometers to change the amplitudes of the signals. For this part, I suspect from the potentiometers, I know they are very unstable but I somehow have to use them.


3. Then, red part, adds the signals together, nothing fancy.


4. Finaly, the green part is my design to drive an 8 ohms speaker.

Now, when I connect the speaker, I get a noticable noise on the speaker output. It is both understandable from sound and also checked by oscilloscope. I have heatsinks for transistors, and I suspected from them for the reason I explained in my other question.

when I inspect the signals in the circuit via oscilloscope, I see there is some noise on waveforms, while trying to understand where it comes from, I have touched the heatsink (...) It becomes much smooter.

However, then, I thought it might be resulting from something else and wanted to get your opinions about it. What can I do to minimize the noise ? Would soldering things on something like this solve things?

Things to note:

1. I got satisfying results in simulations, everything was as I wanted. However the reality spoiled me.


2. I implement the circuit on a breadboard for now, while prototyping, I suspect it may be bad in terms of noise.


3. I don't know it is relevant or not but the noisy parts are mostly in the upper parts of sinusoidal waves.

Thanks in advance.