I have about two hours in a Cessna 172 so my instructor always managed the radio for me. I found it too loud at some times and too quiet at others. Can I tweak mine without bothering him? I forgot to ask last time. Is this the same for most / all planes or does it vary a lot?
Some modern audio panels allow for independent volume control for pilot (left seat), co-pilot (right seat) and passengers.
There are a lot of audio panels out there, so you'd just have to see if the one in your airplane supports independent volume controls.
Additionally, there is a difference between the intercom (in-airplane communication) and radio (airplane-to-communication frequency) volume controls. Often the panel handles the master volume (the mix of both intercom and comm) volume. Whatever radio you're using (see below for an example using a popular GPS Nav/Comm the Garmin GNS430) will likely have a volume control for the Comm and Nav functions (the Nav - to listen to the audio broadcast from a NavAid). In this case, I set the volume I like on the audio panel and then adjust the Radio volume after.
However, I think all (or 99%) of headsets have their own volume control, either inline on the cord or the adjustment is on the ear cup, so you can always adjust your own volume that way if the audio panel doesn't support it.
Related to all this is the question "what does the squelch do?" Essentially the squelch is the volume threshold needed to activate the mic (notice how you don't have to push a button to talk within the airplane?). If set too low, the noise from the engine will continuously activate the mic, set too high and it won't pick up your voice even if yelling or with the mic close to your mouth. It is usually adjusted by either an outer ring (look at the little diagram on the Garmin 340 where it says SQ), or in the case of the GNS430, you push the volume knob in to adjust it. Other equipment, you pull the knob, so it's really a matter of getting to know your avionics! A friend of mine once said, what you really need to know to fly a plane, is how to work the radio!
Yes you can, on your typical training cessna or piper the intercom and radio volumes are separately controlled. The radio will have its own volume knob and the intercom will have another, like this:
If the radio is fine but the intercom is too loud then turn down the volume on the intercom, and vice versa. If they're both too loud turn down your headset's volume control if you have one. Work with your instructor to find a balance that works for you both.
The other intercom knob is the squelch, and is worth mentioning. If the squelch is too low then you'll get a lot of engine noise in the background, if it's too high then you may not be able to hear yourself. I turn the squelch until the engine noise disappears then then just a bit further.