beer tastes great when put in keg but tastes off after 2 days

Not really sure what is goin on. As the title says the beer tasted great when it was put in the keg but two days later had maybe a plastic off taste. I opened the keg tonight and it tastes that way in the keg. These are stainless 3 gal kegs. used sanitizer then a rinse. I really dont get it.
I was using a standard line when I started kegging then when to a glass lined which took care of the tubing taste. Any input would be greatly appreciated.

PS can co2 cause an off taste?

It could be the 5 orings that need to be replace since the tend to stinks with time.

It could also be the dip tube. It's important to clean it with a brush. Nasty stuff can be found in it !

Are you using sometime more than sanitizer to clean the keg. I had a batch go bad in the keg and it was caused by lack of cleaning the dip tube. You need to clean the keg with hot water and PBW plus make sure the dip tube get cleaned too.

You said sanitized and rinsed. What are you rinsing with and why? Both StarSan and idophore are no rinse sanitizers. StarSan is actually completely neutralized the second beer touches it. You could be reintroducing contaminates with your rinse water. Also. I completely disassemble my kegs between beers to clean and sanitize before reuse. As one of the previous posters mentioned, you can remove the dip tubes and run a small brush up and down to clean the inside of the tubes.

Thanks for responses. I dropped of the Earth for a bit. To answer a couple of questions I rinse with water as I cant take the idea of chemical residue in the keg. Maybe something I need to get over. This is only the second use of the kegs so I dont think there is an oring problem. It is most probably the rinsing with water that is the problem. I never had problems when I bottled beer.

I highly recommend a Mark's Kegwasher (or a home-made variant) and Five Star PBW for cleaning the kegs properly (including dip tube and both liquid and gas body connects). Oxyclean can also be used, although unless you rinse really well (which you should be doing anyway), it too can leave an odor.

Then run Five-Star Saniclean through the kegwasher to both sanitize and deodorize the keg, again including dip tube and ball locks. As previously mentioned, just leave a bit of Saniclean in the keg between uses, then dump out the excess right before kegging up the next batch. If you feel you absolutely have to rinse, ONLY use boiled water.

Also, I've never heard of this, but wonder if the odor/flavor could be coming from the CO2 tank? Not sure what kind of processing is involved in making CO2, but it seems possible this could become contaminated with some sort of odor, due to plastic gaskets, machine oils, etc...?

I recently had some serious off-tastes created by "bad tubing" in the kegerator.  The tubing itself was off-gassing so bad that it affected the taste of the beer.  Once I changed out all the bad tubing and sanitzed, the taste went away.  Check the tubing from the CO2 tank and to the tower/keg tap for bad smells/off-gassing.