Each car has various paint jobs that are unlocked as you play the game.
They will not show as "new" with the exclamation point until the appropriate car is selected.
Select each car (equipping it), then move to the paint job tab to see the new paint jobs that are unlocked.
gaming.stackexchange.com/users/33865/Ryan
Select every car and go trough all the tabs.
It's something unlocked for another car.
gaming.stackexchange.com/users/132203/Иво Недев
It's a bug, I have all the DLCs that come with the game, and I have everything checked out, just like you.
But the exclamation point is still there.
I still don't know why they haven't fixed it.
Maybe no one has reported it, who knows?
But I know for sure that it is a bug.
Edit
: Check every car and every decal on it, since all cars unlock new decals and it doesn't put an exclamation point on it.
gaming.stackexchange.com/users/147245/Sain
It probably has something to do with the new NBA adds.
Have you tried navigating through all the tabs to see if there's something new that might not have been "marked"?
gaming.stackexchange.com/users/83919/Mani5556
I had this issue for a while, the problem was that I had unlocked the Royal decal for the Dominus (a DLC car that I did not have).
The way I fixed it was going onto the Manage Inventory tab in garage and scrolling through the items until I found it, then hover over it and the exclamation mark was gone.
gaming.stackexchange.com/users/117990/Nickz2
It apparently is DLC-related, though the specific culprit seems to vary from person to person.
Some people have had success by doing this:
Close the game (if it's open).
Go into your Steam library and uncheck/disable all the DLC.
Open the game, then close it again.
Re-check/re-enable your DLC.
Open the game.
It should hopefully be fixed by this point.
gaming.stackexchange.com/users/147683/Churchbus
1)
Disable Steam Cloud Save: Open Steam Click on the "Library" tab Right-click "Rocket League"
then click "Properties" In the Properties window
click the "Updates" tab Under "Steam Cloud" un-check "Enable Steam Cloud synchronization for Rocket League" Click Close 2)
Delete Local Save:
Open
My Documents\My Games\Rocket League\TAGame\SaveData\DBE_Production Delete both ".save" documents *
NOTE: This will remove all customization!
This includes graphic settings, vehicle presets, and any UI changes!
It will not remove any items / vehicles that have been acquired.
Close the window 3)
Start Rocket League Verify that all the customization options have been reset (and the yellow exclamation point is gone).
4)
Exit Rocket League 5)
Enable Steam Cloud using the procedure in Step 1.
gaming.stackexchange.com/users/183701/Raksul
When you enter the main Rocket League Window.    You will notice I have a Yellow Exclamation Mark under Garage Menu Link.  But when you enter the Garage Menu, Nothing is there for me to highlight or check???    Am I going crazy? or is this a bug of some kind?   Edit: Issue has been going on for months.
Why do I still have a Yellow Attention Logo on Garage Tab?
gaming.stackexchange.com
<rocket-league>
gaming.stackexchange.com/questions/264555
gaming.stackexchange.com/users/69259/Sickest
It's something unlocked for another car. Check every car and every decal on it, since all cars unlock new decals and it doesn't put an exclamation point on it.  It seems that whenever there's something new unlocked, the yellow attention logo will appear.
Players suggest that there is an unlocked item. While someone else believes that it's a bug.