Macros Really Slow The Another Macros Is Run

I have two macros. Macros 1 opens another excel file, counts the number of rows it has, inserts that number of rows into the master file and then copies the data over. Key code as follows (x3 for 3 worksheets)...
For k = 1 To numrows
Selection.EntireRow.Insert
Next k

Macros 2 'cleans' the appended data by systematically going through each row, checking if certain cells have data, and if not deletes the rows. Key code as follows (x3 for 3 worksheets)...

For l = lastrow To 12 Step -1
If WorksheetFunction.CountA(Range("B" & l & ":C" & l)) = 0 Then
Rows(l & ":" & l).Select
Selection.Delete Shift:=xlUp
edelrows = edelrows + 1
End If
Next l

Here's the weirdness. macros 1 runs fairly quick the first time out (few seconds). Macros 2 takes about 2 minutes to run (which I'm fine with). However, when I run macros 1 AFTER running Macros 2, Macros 1 goes from taking a few seconds to a few minutes.