Tires: Tires and noise, 17 inch wheels, scrape marks

Question
QUESTION: I read the post on wheels bearing vs. tires and I have a similar problem.  I just put on new continental 225 45 17 tires on my jetta.  I put 2 on the front first on new wheels and no problem.  I put the two on the back just this week and now I have a noise/hum.  At seventy I put the transmission in neutral and lets the rev's drop to idle and sound still the same so not engine.  The noise started when I put the two tires on the back (They are on new 17 inch wheels also.  One of the continental tires did have a nail and discount tire plus it and spun balances all of the tires.  Can't figure it out?

ANSWER: Jon,

There's some bits of missing information that are going to be necessary to resolving this.

1)  I am unclear if the tires that were put on the front were new or not.  If not new, how many miles were on them.

2)  I am also unclear if the tires put on the rear were new or not.

3)  How much time elapsed between the front tires being put on and the rear tires being put on.

Also, as a diagnostic test, I suggest you take the front tires and put them on the back, and take the back tires and put them on the front.  See if the noise moves with the tires.  Also check on the inside of the wheels and the brake caliper for scrape marks on the inside - just to make sure that is not the problem.

---------- FOLLOW-UP ----------

QUESTION: Thanks - I am going to go by discount tire today to have the cinch up the rear tires today and will check for scrapes.  To answer the other questions-I bought the 4 continentals used from an Auto Yard I've used for years that specializes in foreign cars.  I picked up the first two that went on the front two weeks prior to the final tires arriving.  These had approx. 90% of wear left(came off wrecked Audi).  I picked up the other two and put them on about two weeks later(on back)-prior to this no noise).  These had approx. 80% wear left.  The one that required a plug for a nail was one of these two and is on the back.  There was also a small amount of stress cracks (about one inch from the nail that we noticed).  I ordered another two continentals as we discussed this possibly becoming a problem?  Your thoughts

Answer
Jon,

I'm going to guess that the second set of used tires have irregular wear on them - and that's the source of the noise.  You can confirm this by swapping the tires front to rear, and if the noise moves it was the tires.

BTW, you are aware you are supposed to have the best tires on the rear - right?  That means you need to do the swap anyway.

Irregular wear will work it self out gradually, and since you need to rotate the tires, by the time they are ready for the next rotation (5K or 8K from now) the irregular wear will be mostly gone.

Also, I hope you realize that plugs are not an acceptable repair.  They tend to develop leaks and they give you no warning that that is about to happen until it is too late.  The proper repair is a plug/patch combination.  Since Discount Tire is going to do the swap, why not have them do the repair correctly. (And if they say a plug is an acceptable repair, please tell me the store number, so I can inform their corporate headquarters).