So, at about 125,000 miles few weeks ago had transmission and brake fluid replaced. 2012 Civic. Car drove great before that, great after that.

However, maybe a week later (or a bit less), started to hear odd sound and can't place it.

Sounds almost like dragging muffler (but muffler seems secure and fine). Also sort of sounds like A/C unit is falling out of car. (Basically kind of hard to explain sound). Sounds "metallic" but that's all I got to go on. But, no lights on dash, no vibrations, car seems "fine" other than sound which lasts 10-20 seconds.

So far has happened at super low speeds (under 20mph for sure, maybe under 5mph)...every time so far has happened when accelerating from a stop (or from parking).

Drove car several times this morning, no issues. Parked car. Got out, found place not open, got back in car....then sound started. Radio was off and A/C was off. Slowed down even more to try to hear where sound coming from...and sounds like "underneath car"...then goes away. Then do exact same thing several times, and can't reproduce. Drove it several times since and no sound. And again, it's just a sound...no shimmy, no vibration, no nothing but sound (so far).

Can't take to mechanic until have more information...as again gone many days between sounds - they could currently have it a week and not hear it. This has happened once, maybe twice in one week every week for past 3 weeks or so.

So posting here to see if anyone has ideas or suggestions. Thanks!