Frigidaire FAH086N1T Thru-Wall/Window Air Conditioner

Not really just let unit run and watch what causing the rattling sound.
Maybe unit is not level or even fan blade bent

With these removable units, you must be very careful, the circular mechanism that does the running of the Y motion need to be properly alligned. You need to perhaps put the back of a knife in it and adjust until all the parts align, Then it must click in easily. If you have forced it in the clip will not release. you need to rattle it a little.

alternator bearings are shot. remove and replace alternator. When you have the belt of spin alt pulley listn for noise it should be quiet and smooth to spin.

Start with changing the oil. The oil filter might be plugged.

try U joints or check all you heat shielding on your exhaust it might be harmonic. My 96 300zx rattles alot when i give it some gas and it sounds like tranny but the trans seems to be smooth for the most part and the clutch is relatively new. also check your trans mount. i've seen bolts get loose and it wont knock but it will rattle.

If O2 sensor is bad it can cause Rough running. Are you sure it is the O2 sensor ratteling? Have you taken it out to hear Rattle? Is it loose? I have not Hears an O2 Sensor rattle. I have heard Converters Rattle. over time Inner Material of converter will Not have a tight fit due to heating and cooling. expanding and contracting. carses some of the material to wear away. Causing the it to rattle. and can cause rough running also.

you have to open the unit up or atleast see if the fan is failing. The blower motor is usually a double shaft and cool the compressor and also blows the air across the evaporator. Look for the air to stop blowing then the compressor to shake from overheating.

If it does not make the noise when the fan is ruunin you may ahve abroken sping in the compressor. Make sure you Window unit is level. If not the compressor will knock on the inside. Rusty

These are infamous for blowing bearings, short term try putting molyslip in the gearbox (use the green molyslip) and top up oil if low. Eventually a rebuild will be needed

If the unit has been working fine for a long time and then you suddenly have this issue, the angle you have the unit set at is probably fine, but you probably have a blockage of dirt/mud/sludge/whatever that is keeping it from draining properly. Here's what you have to do...

For safety... turn the unit OFF and UNPLUG IT.
Open the front gate and remove the air filter. Next, remove the entire front gate from the unit (probably at least one screw to remove first - mine was in the middle, just under wher the bottom of the air filter sits). With the gate removed you should have access to locate your blockage problem.

There is a hole that allows the water to drain from the front of the unit (the part that is inside your house) to the back of the unit (the part that hangs outside your house) and eventually out of a drain hole in the rear. Chances are that this hole is clogged. So, when the water fills up in the front drip tray it has no access to drain to the back. Consequently, the water builds up in the fan area which causes the rattling noise and the water being picked up by the fan and blown out of the vent. If left too long, it will overflow the front drip tray and make a mess in your house.

On my unit, the hole was on the far left side (if your are in your house and facing the AC unit) of the drip tray. You can use a piece of coathanger wire, or some other long thin instrument to push the blockage through to the rear. Once this pathway from the front of the unit to the back of the unit is clear, your problem should be solved. You will probably still get the sound and water sputter out of the front for a little while until the water that is in the fan area drains/dries out, but it should return to normal soon.

It is probably best to actually remove the unit from the window and take the cover off of it and really clean it out, but that is obviously a much more involved task. If you have a hose, that's fine and will help. Water won't hurt the unit - just keep it away from the electronics (the controls/display/cord). You should also be carful not to bend any of the tiny metal fins... that's just as bad as (actually worse than) being blocked by dirt/dust. And obviously, allow the unit to dry before you put the cover back on and put it back in your window and plug it in to run it. If you are willing to put in the extra time and effort, you can do a more thorough cleaning job, which would help to prevent the problem from happening again too soon. There's no way to prevent dirt/dust from building up in the unit. Once water/moisture is added to the mix, you're dealing with mud/sludge, which is going to eventually block that small drain path. The only solution is to clean it out once in a while.

I figured this out the hard way. I took the thing out of the window cleaned it (not as thoroughly as I thought) and put it back in and then did it all again. The third time I actually found the hole that was blocked. If it hadn't been such a pain taking it all apart and cleaning it the first two times I would have laughed at myself for missing it.

Good luck! Hope this helps!