AIDS is not a "symptom", it's a medical syndrome.

A medical syndrome is a set of medical symptoms that are usually (although not always) caused by a single disease pathology.

In the case of AIDS, it is only caused by HIV infection and progression to the point where specific cells of your immune system (CD4+ T-cells) fall below a critical threshold.

You can if you live on a farm and have a fireplace or a wood-buring stove. However,

• there are more people today than in medieval times;
• they are packed into cities;
• those dwellings do not typically permit the burning of coal or wood for heat (they use modern gas-fired forced air and steam heating systems, most of which also require electricity to operate);
• the wood consumption for the population would require significant deforestation, even if everyone had a wood-buring stove (which they do not);

So, you can't use medieval heating methods (burning wood) in densly packed cities whose dwellings aren't designed to burn wood for heat.

Systems of vibrations occurring within atoms that make up solids or liquids.

Example: I strike the end of a metal bar with a hammer. That hammer causes atoms at the stuck end to compress slightly, which, in turn, compresses the adjacent, non-compressed atoms. A compression wave (phonon) then travels along the bar, causing the opposite end to vibrate.

Yes, it's called passive sonar.

Not only that, the US Navy has an array of hydrophones (underwater microphones) across the globe that can not only pinpoint the location of virtually every ship/sub in the world but have developed extraordinarily sophisticated algorithms to decode the unique acoustic signature of every ship. Said another way: all ships emit sound (engine, prop moving through water, etc.) and every ship (even ships made from the same design/blueprint) have enough unique differences that result in slightly different sounds when in operation.

Fun fact: this system has also been used to track whales - groups of whales and individual whales with their unique acoustic ID.

Gut microbiome is established after birth - during birth (passing through the vagina), immediately after birth (sucking on mom's teat), and at all times post-birth (touching things, people, putting hands in mouth). All of this ends up being swallowed and establishing the gut microbiome.