Mysterious tapping sound/pulsation?

[s4ean]

So I did a bit of searching and I'm not sure if anyone's tread describes the issue I'm having. I'm hearing what sounds like a tapping sound, or perhaps something shaking from the driver side of the vehicle. I can only hear it one of 2 ways, from inside the vehicle, or outside with me ear near the front wheel well. I can hear it from underneath the vehicle near the wheel well, or even with my ear pressed against the fender. The sound only occurs at idle, disappearing "almost" immediately upon giving it gas. It only occurs when sitting still. I can feel it as well through the pedals in the floor and slightly in the steering wheel. I thought motor mounts as I know they are worn, but I really can't see the two being connected (unless there's a bad mount there hidden from view that's completely shot). It's not a constant problem, but a reoccurring one that's happening more and more frequently, and it's reached the point of "more often than not".

This may or may not be related, but yesterday when I went to start the car, there was a click and nothing, all power was lost. After a little inspect I found one of the bolts on my battery terminal had become loose. Tightened and problem solved, but I've no idea how it would all of a sudden have loosed, unless the vibrations shook it loose somehow. The battery doesn't appear to be shaking and is tightly installed as well. I can see nothing shaking or moving at all under the hood. The only thing I believe that moves on that side (V6) is the transmission right? It seems to operate without any problem. 120k on the vehicle. What could this be? What could've come loose?

S/N: I also noticed what looked like an old fluid spill of some sort on the back of the transmission casing, can't tell whether it's old or fresh... but the top of the battery was possibly wet at some point as well and it could've come from there? Any help would be appreciated! My Galant tends to have all those unique issues no one has encountered.

[s4ean]

No ideas? Anyone? There's a motor mount located under the battery tray isn't there? Could it cause vibration/shaking only at idle?

[wetamup2k3g]

It could be a motor mount. On my old Galant it did make a sound much like you describe, but only in gear while stopped while the engine was still cold. It was more high-pitched though, not as much of a tapping sound.

[s4ean]

The sound is more noticeable while in gear actually, and only when stopped and idling. But it's definitely low pitched, and there doesn't appear to be any difference whether it's warmed up or not.

[thegalant]

Is it coming from the engine? Could be the lash adjusters? If the clicking sound isn't in pair with the engine vibrating then it's not related. Put your e brake on all the way and have some one rev the engine while your underneath and find the sound. ALso brace the front wheels just in case. Thats how your going to figure this out, get underneath and make the sound happen while you or some one searches for the location of the sound.

[s4ean]

Well that's the thing... the sound and vibration stop completely when revving, it only makes it at idle. I can hear it underneath around the wheel well, and from inside the vehicle, but not near the engine itself. You can feel it in the steering wheel, gas & brake pedals, and I suppose just sitting in the car (it's stronger and louder sometimes, no consistency) as well. The other big issue, it doesn't always do it, and I haven't figured out what triggers it. I'll stop at a traffic light, and it'll start; drive to the next light, stop and it'll be fine.

[8thLS6]

I'm thinking mount..sounds like what I'm dealing with in my right hand mount. Vibration not so much, but the sounds and when they occur, yea. And I just had a shop tell me today that's what it was