All else being equal, a faster card means the device it's in spends less time sending data to or reading data from the card.
That of course is based on the assumption said device can even take advantage of a faster card.
I'm not certain with SD based cards if this is still true but I know cards like Compact Flash could only be written too and from as fast as the device could operate so purchasing a faster card did not always mean your data transfer rates would also increase. I know this was true with early day digital cameras. If they supported a faster card, that was usually a selling point printed on the box or the devices sales leaflet.
Changing the batteries will not help SD card issues.
Try a different card. And make sure the contacts in the card slot and on the card are clean.
Speaking of this, does anyone actually make an SD or microSD card slot cleaning card?
I could see something like this coming in handy if dirty contacts inside a card slot do develop resistance from who knows what, nicotine film from smoking, liquids entering the slot from a card dropped in soda etc.
I think it would be virtually impossible for someone to actually clean a card slots contacts today without using something like a DeoxIT type spray cleaner which many know, can ruin certain plastics and other finishes and sometimes even cause much more permanent damage.
Something more along the lines of a really super fine abrasive for those slots contacts that may have some type of buildup on them. Something similar to the "dry" type floppy disk head cleaner disks you used to be able to purchase. And maybe a wet "alcohol" (or similar) based cleaner for slots that have had known liquids enter into them somehow.
Of course cleaning an actual cards contacts can be done with little effort with a pencil eraser and caution but not out of the question.
I know for a fact that the connection between card and slot can cause noise to appear in an external amplified or unamplified speaker attached to a 536HP. Simply removing and reinserting a microSD card in the 536's slot is often enough to clean up the contacts and allow a better connection which produces less or no noise in the speaker.
This is not related to the headphone noise issue.
This noise I'm speaking of can sometimes be heard easier by using certain Class 10 or faster cards in at least the 536HP model. It is more pronounced when using amplified speakers' setup for BTL outputs also.
Simply reinserting the microSD card can sometimes eliminate the digital artifacts that one can hear while the scanner is doing its thing even with the volume all the way down.
Observing this with my own ears has always led me to believe there is some form of electrical resistance between the SD card and the slots contacts. By reinserting the card, it seems to cleanup the contacts enough to make a difference but not always.