ok im opening pandoras box here.(treatment vs framed wall art)

The pictures on your wall are vibrating in response and sympathy to your room's 3 primary resonate frequencies being excited or over pressurized 

Every room has 3 primary resonate frequencies based on the room's physical dimensions between the parallel walls for it's height .. width and length  

When excessive pressure builds up at these specific frequencies the wall or walls will vibrate shaking your pictures along with other items placed in your room such as a drinking glasses or pictures placed  on a table or  shelf

 Your room operates in two completely different states or conditions above and below the rooms transition point also known as the Schroder frequency 

Above your room's transition point the frequencies coming from your speakers act as RAYs or BEAMs of LIGHT and project from your speakers in a straight line until they come into contact with a solid object ... there they are reflected 

The frequencies above the transition point behave this way because their length peak to peak physically fits with in the room's dimensions 

Frequencies below the room's transition point are to long peak to peak and WILL NOT physically fit within the rooms dimension so instead of behaving like RAYS they pressurize the room instead of bouncing around it  

Lets say for sake of argument that your room was 7x12x18 ... your room's 3 primary resonate frequencies would be 80hz x 47hz x 31hz based on those dimensions ... anytime your system generated one of these frequencies or notes it would excite the corresponding wall based on the room's dimension and primary resonate frequency point

You have two issues to deal with ... the vibrating pictures can be reduced by employing a 3 channel parametric EQ ... here you would first identify the primary resonate room frequencies and reduce the excessive pressure build up by placing a cut at that frequency ... this would reduce the energy at that frequency and reduce wall vibrations and lessen the picture rattling 

The brightness could be caused by a number of things including your equipment make up ... but if you move the pictures out of the first reflection point of the speakers ... you may be able to reduce some of the brightness 

Don't forget in addition to the side wall first reflection points (which most are aware of ) you also have first reflection points at the back wall .. front wall and ceiling and floor 

As I doubt you have any pictures placed or hanging on the ceiling or floor I would look to relocate the pictures on the side wall back wall and front wall from the speaker's first reflection point 

The problem is a bit more complicated and not quite as clean and clear cut as I've presented it ... there is a ZONE of TRANSITION that is between the  Schroder Frequency where the frequencies begin to transition between being RAYs to PRESSURIZING the room that is very tricky Zone to deal with ... also Echo Slap parallel to speakers and seating position between the two parallel side walls and also front and back walls should not have pictures placed at that point

Understanding how and why your room behaves is the first step in trying to correct the problems cause d by it

Brightness is a condition that exists in a system when there is excessive treble energy relative to the rest of the audio spectrum ... it is an out of balanced condition that can be caused by either your equipment or generated from your room 

Digital components with high amounts of jitter can produce this bright condition ... RF sneaking into the signal path can cause brightness ... even uncontrolled vibration can raise treble energy  

Poorly designed components that don't produce adequate amounts of bass can also cause the treble to stick or stand out and present a bright or tipped up condition  

This bright condition can also be caused by your room when conditions cause extended modal ringing in the high frequencies ... here you have extra long RT60 times were the note just lingers more than it should  

The two most common perpetrators in the room are ... Echo Slap were the sound energy just keeps bouncing and lingering to long  between two parallel walls ...  and the wall/ceiling interface where the wall meets the ceiling ... here energy traveling up the wall combines with energy traveling along the ceiling in what is known as the laminar effect combine at the wall ceiling interface and are reflected back into the room ... unfortunately the combined energy that is reflected back into the room has much more energy than the original note  and causes the note to linger or ring well beyond it's normal or natural decay time  

If there is any problems created by your glass framed pictures it's a would be caused if your pictures are hung at the point where the direct wave above the room's transition point coming from the speaker strikes the side wall  

The reflection off the glass would be reflected at a different rate than if the wave struck the sheet rock wall ... now the problem is of different arrival times at the listening position of the direct wave from the speaker arriving ahead of the reflected wave off the wall ... the glass may reflect more energy than the sheetrock would have  

Your ear would perceive this as two separate notes because the same note arrives at different time intervals ... this would blur the imaging .. mask low level detail and effect the sound stage but I doubt very much that it would tip or increase treble energy 

As Geoff has suggested try removing the pictures and I'll bet your room still sounds bright as I think the brightness is being caused by some other condition  

One more point of interest is even if you remove the pictures from the room ... the room will still respond and vibrate in sympathy to it's primary resonate frequencies based on the rooms dimension  

The problem here is every primary note has harmonics and the harmonics from this low frequency distortion can easily reach up into the midrange and lower treble coloring both 

Success in audio will only come when you realize that the room and not you is in control ... so you need to take control of your room's anomaly