I have a pair of earphones with silicone cushions, so they do a pretty good job of sealing out external noise (they are not noise-cancelling headphones).
When I have them on, especially when there is no music playing, I have this extremely heightened awareness of my own footsteps, sometimes I even notice my heartbeat, and chewing sounds like hell of a racket.
Why do I not notice these sounds in the least from day to day, but when my ears are plugged up they seem very loud?
Same here - I dated a guy for a short time who snored…LOUD. I used earplugs but they were almost just as annoying because then I could hear my own heart beating, plus they hurt my ears by the morning. You’re not the only one to notice this.
WAG. The ‘self-generated’ sounds you mention are all ones that could reach your eardrums through your body, without needing to pass through the air in the auditory canal (which is the approach that your earphones seal out.)
Thus, you’re hearing them at nearly the same volume as ever, and they seem louder in comparison with ambient noise from further away that is getting muffled and damped down by the earphones.
Your ears have a “gain control”, the outer hair cells of the cochlea, that act as a frequency-selective amplifier that can be selectively tuned and turned up and down by the brain. Presumably, when the plugs are in the brain turns the amplifier up to 11, and tunes it to the sounds that are available, mainly those transmitted to your ear through your body rather than through the air. However, this is essentially an attentional effect, and you will probably soon find that you can learn to ignore these sounds, which probably means that the amplifier is being turned down and de-tuned to the relevant frequencies (although there is also a lot of complex attentional control going on entirely within the sensory processing areas of the brain).
I habitually sleep with ear plugs and am not bothered by ordinary bodily sounds, which I have long since learned to ignore. However, if there is something unusual, like a wheeze in my breathing due to a cold, it can be very annoying. Since I got used to the earplugs, if I don’t wear then, even if it is otherwise quiet, I find I am sometimes kept awake by the sound of my own breathing, but that is an airborne sound rather than a bodily one, and blocked out by the plugs.
njtt beat me to it.
There are at least 3 different mechanisms of gain control, ignoring what happens in the brain (the “attention” aspect mentioned by njtt).
But the latter two are usually in play when sound levels are quite loud. If you’ve ever felt your ears “squinch” when a loud sound goes away, that’s one of the muscles relaxing.
The one I talked about - the tunable amplifier created by the activity of the outer hair cells of the cochlea - makes four, and this cohlear amplifier (almost certainly) does operate to make quiet sounds louder, rather than just to make loud sounds quieter. (It is an actual amplifier, injecting extra energy into the signal.)