My 1997 Jaguar XJ6 with 55K miles has squeal noise since purchased in January 2018. The sqeal noise lasted from 5 to 15 seconds.
The squeal noise was not result from:

1. I searched this forum and tested harmonic balancer and it was not an issue.
2. I removed the AC belt to determine if this AC belt or idle pulleys caused noise and they were not.
3. I remove alternator and water pump belt and noticed water pump had some free play. As such, I went ahead and replaced water pump.

Since the Jaguar been sat in a garage for a while. I went ahead and replaced both belts, idle pulley, and water pump. However, the noise did not goes away. After reading and searching, I was able to pin point the squeal noise was resulted from the secondary air injection pump. I monumentally disconnect the main harness to the pump and the noise went away when car started. X300 uses same secondary injection pump with mid 90s vehicles from GM such as Corvette, Camaro, Trans Am and Oldsmobile. I kicked myself since there was a X300 in junk yard couple months ago. I bought bunch of old parts from this Jaguar but I did not purchased the used pump for $11.00

 

I pin point to the Emission pump area that caused pitch noise. However, it appeared that the main cause was from a check valve that prevent hot exhaust from entering the emission pump. The check valve is connected in series to pump and to exhaust. The check valve is located in the valley, on driver side fender and engine; and below the air filter inlet tube connected to throttle body. There is no clearance or leverage for me to remove this check valve even with the air inlet tube removed. The check valve is connected to exhaust via an flex aluminum tubing. I almost certain will bend or break this tube if not careful. I do have all the tools in the world but could not removed check valve.

https://www.ebay.com/itm/Air-Pump-Ch...53.m1438.l2649

I am thinking of using and air tool and cut the aluminium tube to remove defect check valve and used this check valve shown below. I will connect cut aluminum tubing to check valve via silicon tubing and clamps. ANY OTHER SUGGESTIONS?

https://www.ebay.com/itm/Air-Pump-Ch...53.m1438.l2649