Toilet Makes Hissing Sound

About three weeks ago my, water heater died and we had it replaced. When they did so, they had to add a tank on the top of the water heater that was not their before (http://www.lowes.com/lowes/lkn? action=productDetail&productId0680-48324-LET-2&lpage=none not the exact one but its basically the same thing). Its now required in my city due to some water meter changes the city made. Anyway, as soon as the guys (yes I hired someone) finished the toilet started to hiss. I don't think that an abnormal amount of water is going from the tank to the bowl so its not a constant refilling issue. If I close the shut off value the noise stops, and when I open the value the noise starts again. If I leave the valve open for a few days the noise gets louder (it gets to the point of annoying and then I close the valve). Here is another strange point. I was changing a hot water shut off value in the kitchen, and I noticed when I close the hot water valve coming from the water heater the noise in the toilet jumped.
Anyway, whats going on to make the hissing noise?
Should I just get one of those replacement kits at Home Depot or Lowes and see what happens (noticed they are less than $15).
John
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On 19 Mar 2007 14:12:57 -0700, "runsrealfast"

Is the water level in the tank overflowing? Or is the tank refilling without anyone flushing it?
later,
tom @ www.MedJobSite.com
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No really overflowing. I have noticed that there is more water in the tank than there should be (water level is above the hard water stains).

I don't think the tank is refilling itself. I did the dye test a few weeks ago and after 20 minutes had a very tiny bit of dyed water in the bowl.
John
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On 20 Mar 2007 12:22:16 -0700, "runsrealfast"

IMHO:
Maybe the tank is draining, per your test, and the fill valve is now throttled to maintain the level. Meaning a little is leaking by the flapper, and then some water is being entered into the tank and that is making the sound.
Since I don't like wasting resources, since it usually comes as wasting money for me, I would check the flapper. It could just need a wiping down with a clean rag. If not have someone who knows what they are doing to help diagnose/fix the problem.
Just a guess...
tom @ www.Consolidated-Loans.info
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On Tue, 20 Mar 2007 17:55:57 -0500, Jeff Wisnia

A good question could be, after the stop valve is closed, does the hissing sound decrease with time, and then disapears?
Just an observation....
tom @ www.FreeCreditReportAdvice.com

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On Mon, 19 Mar 2007 14:12:57 -0700, runsrealfast wrote:

So your saying when the toiled is filling it now makes a new noise? This is likely not a problem with the toilet but with the valve/hose to the toilet. Probably the pressure in the pipes has changed and now it hisses. I reinstalled guts in most of my toilets since they all failed (3 years old, FUCK Gerber). But the hose to the toilet was plastic and I think when I reinstalled them, I did not have them straight enough. So water passing through them would make a LOUD sound while the toilet filled. Took a while to figure that one out.
Also on the master bath toilet there was some debris inside the shutoff valve. No idea how that got there.

Its more of a pressure problem and likely the hissing is not from inside the tank but at the shutoff valve. Make sure the hose is not crimped.
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