Noticed in the last few years that on many professional shot/produced etc. shows, the ambient sound levels are not even.

For instance, watching "The Office" recently, when people are talking, it drops out completely (or way down). When they stop, becomes very audible. Sometimes even between words.


Is this the mix or some kind of compression effect during transmission? Or my TV?

Very unlikely that it's your TV.

No way to be entirely sure about the track, without listening directly to the track. But I don't know of any good reason it would have been mixed that way.

Most likely it's compression at the TV station to keep the levels more consistently higher. Bad audio practice (in terms of accurate fidelity), but typical broadcasting practice.