Auotmatic transmission makes rattling sound in park?

It sounds like you have a cracked flex plate but if you upload a short video of the noise, I can tell for sure what is wrong.

I will make the video later. By the way, I have abrand-new external transmission filter that I have not changed yet. Does it matter if I change it or not?

video1

video2

video3

Video1 and 2 sound closer to normal? Video3 makes a sharp noise at the beginning and the end.I could not get the rattling sound from yesterday.If you need more videos,let me know.

Yes, you need to change the external filter. To me it sounds more like a catalytic converter has broken apart internally, I would shut the engine off and then use a rubber hammer to tap on the exhaust system to see if you duplicate the noise. thanks for the videos they helped. Let me know.

How can a catalytic converter affect the auto transmission?The car wouldn't go and gave me P0730 and P0795.I thought they are 2 separate issues.I'm confused.I will change the external filter.

Yep, it would cause those codes I was going off of the noise, you might have two problems.

P0730 - Incorrect Gear Ratio:

P0795 - Pressure Control Solenoid “C” Malfunction:

So, what happens is the front fluid pump can go out and cause solenoid codes or you have a bad connection. Also, with the p0730 have you replaced the counter shaft sensor? I have seen this sensor get weak and cause this code. Here is a guide to help check the connection and the wiring diagrams so you can see which wires to test.

https://www.2carpros.com/articles/how-to-check-wiring

Check out the images (below). Please let us know what happens.

I'm still confused. Do you mean the P0420 is related to the auto trans codes? I also heard the rattling sound from the driver's side (the transmission) before. And the catalytic converter is on the passenger's side. On the main shaft and countershaft speed sensors you mentioned, I can't find them online even at the Honda parts websites. What are their correct names or part numbers to search for? If I can't find any, should I just remove and clean them and put them back? Is there any way to test them while removed? The main is A and counter is B? What about the cracked flex plate now?

I also have a P780 code with D blinking when I drove around the block before I changed solenoid C(B+C).What else I should check?

I checked again today and noticed a have a small leak at the cover bottom of part #17 of the picture attached which I've never noticed before. And it's in the general area where I heard the rattling sound before. Partt 17 is the plug which attaches to 4 connectors of solenoids A,B,C&E(no D).I've found a set of these solenoids online with 5 solenoids(A,B,C,D&E) which they say will fit my car).Should I give it a try,I just use only 4 solenoids?

Sorry,it's #17 and 9 in the picture.

The pressure C malfunction can be a pressure issue as well and with an incorrect ratio it is telling us the transmission may need to be rebuilt FYI.