Went to see a 2007 XKR Convertible with 70k miles, great shape with some things I have questions about.

Primarily a mechanical issue I noticed.

While the car idled, there was a intermittent knocking/rattling in what sounded like the supercharger. While under load it sounded like ignition pinging/rattling.

Any ideas, or common issues this can relate to?

Did not have any CEL on.

Thank you in advance.

 

RUN AWAY!
No, seriously, unless it is REALLY CHEAP ($10,000 US), you are asking for trouble.
Of course, you fail to put down number of owners, condition inside and out, or even a link to the site where you found it.
There are only a few inherent problems with the X150 models, and none of them regard the supercharger, knocking, pinging or rattling.

 

asking 17,500 firm, nice shape overall no dings, nice interior, nice top, good tires, ac works and has had the leaks in the ac fixed. overall about 7/12-10 clean title and no accident history

 

What I would advise since you seem to like the car, have a Pre-Purchase Inspection done by a qualified Jaguar mechanic, usually at a dealer. They cost right around $200. Cheap for peace of mind.
Is there any DOCUMENTED service completed? Car Faxes are hardly 100% accurate, but they sometimes can shed some light on certain things, like Auction Sales, possible collisions, number of owners and such forth.
Depending on who your seller is, private party, independent dealer or a certified Jaguar dealer, the cost of the inspection could be included in the sales price or used for negotiation.
At $17,500. it appears to be about $10,000 below the going rate. Why is that?
You haven't stated where you are, it's a good thing to have your location in your profile so people won't need to ask you in order to maybe give certain advice and such.
If you DO end up buying this or any OTHER Jaguar, glad to have you in the Forum!

 

I agree here

 

I just quickly searched ebay and it looks like the 4.2 sc motor sells for around 4 grand. Depends on how handy you are!

 

That sounds scary. I bought my 08 with zero mechanical issues and minimal cosmetic for 17k days ago.

What are the miles? The supercharger belt could be going, which is due at 100k iirc. Modern AC systems should be able to last considerably longer. Two of my trucks have 250k+, from early 2000's, and have perfectly working AC, as does my wife's old '04 nissan sentra.

Drop $40 on the carfax, get a history, crawl over the car. Drive it in numerous situations. Take a day or three. Don't drive it the first day, is the biggest mistake. Look at it, test all the systems. Get a good idea of physical condition. Then drive it. Go fast, slow, all over.

 

Unless you are in the business of fixing engines...I would walk away and go find something that is working perfect. There are plenty of good Jaguars out there with no issues. Why start the day off with a headache?