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I am drawing a block diagram of a mixing system using the code below:

documentclassarticle
usepackagepgfplots

usetikzlibrarypatterns,positioning,calc,shapes,arrows, quotes, angles

begindocument
beginfigure
centering
begintikzpicture
 node [rectangle, draw, minimum width=2cm, minimum height=3cm, color=black, fill=green, inner sep=0cm, label=below:tinyUnmixing System] (unmixing_sys) ;
 node [left=30pt of unmixing_sys.130, draw, circle, color=black, fill=red, minimum size=0.45cm, label=below:tinyMic 1] (mic1);
 node [left=30pt of unmixing_sys.230, draw, circle, color=black, fill=red, minimum size=0.45cm, label=below:tinyMic 2] (mic2);
 node [above left=10pt and 30pt of mic1] (s3)colorblue$s_3(t)$;
 node [below left=10pt and 30pt of mic2] (s1)colorblue$s_1(t)$;
 node (s2) at ($(s1)!0.5!(s3)$) colorblue$s_2(t)$;
 path [anchor=south, draw, -latex'] (s1.0) -- (mic2.180);
 path [anchor=south, draw, -latex'] (s2.0) -- (mic2.180);
 path [anchor=south, draw, -latex'] (s3.0) -- (mic2.180);
 path [anchor=south, draw, -latex'] (s1.0) -- (mic1.180);
 path [anchor=south, draw, -latex'] (s2.0) -- (mic1.180);
 path [anchor=south, draw, -latex'] (s3.0) -- (mic1.180);
 path [anchor=south, draw, -latex'] (mic1.0) edge node [above] $x_1(t)$ (unmixing_sys.130);
 path [anchor=south, draw, -latex'] (mic2.0) edge node [above] $x_2(t)$ (unmixing_sys.230);
 node [right=15pt of unmixing_sys.50] (s1hat) colorblue$hats_1(t)$;
 node [right=15pt of unmixing_sys.0] (s2hat) colorblue$hats_2(t)$;
 node [right=15pt of unmixing_sys.310] (s3hat) colorblue$hats_3(t)$;
 path [anchor=south, draw, -latex'] (unmixing_sys.50) -- (s1hat);
 path [anchor=south, draw, -latex'] (unmixing_sys.0) -- (s2hat);
 path [anchor=south, draw, -latex'] (unmixing_sys.310) -- (s3hat);
endtikzpicture
endfigure
enddocument

I want to get rid of extra arrow heads/notches that can be seen easily on right side on the periphery of the red nodes labelled Mic1 and Mic2. Can someone suggest what I might be doing wrong here? Thanks in advance.

As indicated on page 188 of the TikZ 3.14b manual, to ensure that arrows are only drawn when the path actually exists, simply add the tips=proper option to the tikzpicture environment.

begintikzpicture[tips=proper]

documentclass[tikz,border=5mm]standalone
%usepackagepgfplots

usetikzlibrarypatterns,positioning,calc,shapes,arrows, quotes, angles

begindocument
%beginfigure
%centering
begintikzpicture[tips=proper]
 node [rectangle, draw, minimum width=2cm, minimum height=3cm, color=black, fill=green, inner sep=0cm, label=below:tinyUnmixing System] (unmixing_sys) ;
 node [left=30pt of unmixing_sys.130, draw, circle, color=black, fill=red, minimum size=0.45cm, label=below:tinyMic 1] (mic1);
 node [left=30pt of unmixing_sys.230, draw, circle, color=black, fill=red, minimum size=0.45cm, label=below:tinyMic 2] (mic2);
 node [above left=10pt and 30pt of mic1] (s3)colorblue$s_3(t)$;
 node [below left=10pt and 30pt of mic2] (s1)colorblue$s_1(t)$;
 node (s2) at ($(s1)!0.5!(s3)$) colorblue$s_2(t)$;
 path [anchor=south, draw, -latex'] (s1.0) -- (mic2.180);
 path [anchor=south, draw, -latex'] (s2.0) -- (mic2.180);
 path [anchor=south, draw, -latex'] (s3.0) -- (mic2.180);
 path [anchor=south, draw, -latex'] (s1.0) -- (mic1.180);
 path [anchor=south, draw, -latex'] (s2.0) -- (mic1.180);
 path [anchor=south, draw, -latex'] (s3.0) -- (mic1.180);
 path [anchor=south, draw,blue, -latex'] (mic1.0) edge node [above] $x_1(t)$ (unmixing_sys.130);
 path [anchor=south, draw, -latex'] (mic2.0) edge node [above] $x_2(t)$ (unmixing_sys.230);
 node [right=15pt of unmixing_sys.50] (s1hat) colorblue$hats_1(t)$;
 node [right=15pt of unmixing_sys.0] (s2hat) colorblue$hats_2(t)$;
 node [right=15pt of unmixing_sys.310] (s3hat) colorblue$hats_3(t)$;
 path [anchor=south, draw, -latex'] (unmixing_sys.50) -- (s1hat);
 path [anchor=south, draw, -latex'] (unmixing_sys.0) -- (s2hat);
 path [anchor=south, draw, -latex'] (unmixing_sys.310) -- (s3hat);
endtikzpicture
%endfigure
enddocument

Correct arrows you obtain also if you define edges as:

every edge/.style = draw, -Latex

Off-topic: see if the following code is useful to you:

documentclassarticle
usepackagepgfplots
usetikzlibraryarrows.meta,
 calc,
 positioning

begindocument
 beginfigure
centering
 begintikzpicture[
node distance = 11mm and 13mm,
 ar/.style = draw,-Latex,
 box/.style = draw, minimum width=2cm, minimum height=3cm, fill=green,
 RC/.style = circle, draw, fill=red!30, inner sep=4pt,
 node contents=,
 BN/.style = text=blue,
every label/.style = font=tiny, align=center, inner sep=2pt,
 every edge/.style = ar
 ]
%
node (s1) [BN] $s_3(t)$;
node (s2) [BN,below=of s1] $s_2(t)$;
node (s3) [BN,below=of s2] $s_1(t)$;
%
node (c1) [RC, right=of $(s1)!0.5!(s2)$, label=275:Mic 1];
node (c2) [RC, below=of c1, label=275:Mic 2];
%
node (b1) [box, right=of $(c1)!0.5!(c2)$,
 label=below:Unmixing System] ;
%
draw[ar] (c1 -| b1.east) -- ++ (1,0) node [BN, right] $hats_1(t)$;
draw[ar] (b1.east) -- ++ (1,0) node [BN, right] $hats_2(t)$;
draw[ar] (c2 -| b1.east) -- ++ (1,0) node [BN, right] $hats_3(t)$;
%
draw (s1.east) edge (c1)
 (s1.east) edge (c2)
 (s2.east) edge (c1)
 (s2.east) edge (c2)
 (s3.east) edge (c1)
 (s3.east) edge (c2)
%
 (c1) edge (c1 -| b1.west)
 (c2) edge (c2 -| b1.west)
;
endtikzpicture
 endfigure
enddocument