The tempo match's the speed of fan slowing to a stop. That would indicate a piece of paper/plastic being repeatly hit. Many indoor heat pump coils do have a valve that is nothing more than a slug that moves in one direction to meter refergerant during cool mode then the other direction allowing unobstructed flow in heat mode. I've never seen one do it but it's possible it could viberate but I think the tempo would be much faster. I would use a flashlight to search for object inside squirrel cage. BTW,Harley is an accurate description.

A loose flap like piece of houseing could also be the culprit. Just be sure to cut power off while you are in there. The door safety switch should prevent blower starting but the switch is easily bumped and cause blower to start. Don't ask how I know that. ):

Thanks guys. I've swept out the fan. Turned by hand. Had blower on full time and auto. Turned thermostat to 80 and off to get fan to go at different speeds and I can't get it to make the noise. It does sound like cards in a kids bicycle wheel as he slows down but no sign of a "card" touching this wheel. It not consistent. It happens every day or two. One day it was 15 degrees. Another it was 44.

"Had blower on full time and auto."

Does that mean with fan on full time it make's the noise eventhough fan is continueing to run? I understand the noise only happen's at random times and you are unable to duplicate the behavior. What I want to make certain of is,does it ever do it while fan is set to on? Stated another way,we need to know if noise is associated with compressor going off or fan going off. I want to caution against cycling unit at t-stat. A heat or cool restart too soon (within 3 minutes) can severly harm the compressor on many units. It does no harm to short cycle the fan or run fan continuously for days at a time. To turn fan on and off for testing,set t-stat to off and fan to on,when you remove door fan should stop. To restart fan simple press door switch with finger.

I was just trying to get fan running different speeds to try to trigger the noise but noise did not happen when I was looking for it. Thanks for the tip on the restart issue. The noise seems to happen when the outdoor unit cuts off and the indoor fan turns off. Thanks

can you take a picture from other side of blower motor to show what the blower motor looks like?

It's not a normal noise, even of failure... like bearing failure etc.

You'll have to investigate further.

ah kind of what I thought. It's variable speed DC motor. This may be an early indication of motor starting to head south.

It's very rare these kinds of motors make it past 8 years of operation.

I hope that's not the case...but it does sound like a motor/fan spinning down. I bet that will be expensive to replace. Thx

There isn't much on a Trane system (part wise) that isn't expensive. It's the con game in thinking this brand is some how better than other options, by other manufacturer's.

With that said, all major name brands of HVAC equipment can have ridiculous part pricing, so you have to understand what I am really saying here. Like to say Carrier is so much cheaper than Trane on parts... uh no, get that thinking plumb out of your head. The lesser known brands are what I am talking about.

BUT, the lesser known brands are sometimes not worth it. This is why you use a good licensed HVAC repair guy, like me.... to direct your path. It's a mine field out there ladies and gentlemen.

I serve Katy, Texas area.

I hope my variable speed DC motors last more than 8 years. I own three of them. They will be 8 years old in April.

A replacement of this type of motor will be expensive no matter which brand you choose.

They are very efficient motors, but that efficiency comes with a price tag when the motor fails. Many will state that it's the back end or inverter part of the motor that fails... in my experience it's best to replace both.

I had an American Standard AH unit at my previous home which is more or less the same thing as Trane, just different sticker on the unit. The motor bearings in it seized up. Which is rare for this kind of motor as the inverter part typically is what fails. This unit when it failed was approximately 8.5 years old. Bearings in a standard PSC blower motor can last up to 20 years by comparison.

If you somehow make it beyond 10 years with out replacing one of these motors mike, count yourself lucky.

I was able to remove the top cover where the fan resides while the sound was being heard. It is NOT coming from the fan. It's definitely one of the tubes running into the air handler. The bottom copper tube seems to be the source. Is there a check valve in there or something that could be the source? I also ran the unit in emergency heat mode several hours without the sound.

If it's not the motor it might be drain problem. It sounds like it could be a hammering effect on plumbing. So if the drains aren't proper the suction of the blower will sometimes cause hammer effect.

After listening to the video again this is kind of what it sounds like it might be. But it's merely a guess.